Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
: Looks good. Another approach would be something like a BFP650 follower,
Phil, I was about to suggest that if you've ended up using the
BFP650 by following my example, you might be better off with the BFP640.
Or more modern ones with a higher hFE (I'm fond of the NESG3031 and
NESG4030).
Namely, my choice of BFP650 (and not the then more widely available
BFP640) was driven by the search of the lowest possible R_BB, because
I was deemed to encounter lower source resistances than the 50ohms for
which SiGe devices are generally optimized. I reasoned that the base
geometry of the BFP650, as a medium power device, is more likely yield
a low R_BB. In your applications BFP640 may work better with the "more
ordinary" impedance levels and ambient temperatures.
The "I was about.." part means that I'm somewhat puzzled now that I
looked up the recent Infineon data sheets. The BFP650 is now listed
as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon
model reads RB=6.376 . The preliminary datasheet I have, dated
Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm
wondering how much the device has changed from the versions I've been
using. I seem to recall that also in some other more recent data sheet
versions it was listed as a SiGe, not SiGe:C .
Given the fact that the most recent BFP640 datasheet (dated 2007-05-29)
reads RB=3.129, the BFP650 does not seem to have any noise advantage
any more, either.
In fact, there was a recent paper in the RSI where
the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe,
as compared with my 75 pV/rtHz with BFP650. This is a puzzling result,
actually, because it is better than one would expect in the picture where
u_N originates from the collector shot noise acting on the r_E - provided
that the thermal voltage saturates at ~5..7 meV even when the ambient
temperature keeps going down. According to my data it does saturate in
BFP640 just like it does in all other SiGe's I've tried, when measured by
the transconductance. I'm wondering whether my transistors have always
been oscillating so high that I cannot see it (ie. >27 GHz) and the
V_T saturation is an artefact due to it...
Regards,
Mikko
picosecond test points
Started by ●February 11, 2012
Reply by ●February 12, 20122012-02-12
Reply by ●February 12, 20122012-02-12
Okkim Atnarivik wrote:>the Jena group claim to have achieved 15pV/rtHz with BFP640 in LHe... a typo, sorry, they actually claim 35 pV/rtHz . And they seem to have regenerated the emitter inductively, so the instability hypothesis may indeed be true in my case. Regards, Mikko
Reply by ●February 12, 20122012-02-12
On Feb 11, 5:20=A0pm, "langw...@fonz.dk" <langw...@fonz.dk> wrote:> On 11 Feb., 21:57, John Larkin > > > > > > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > We're designing some laser driver boards, and I thought it would be > > cool to add test points to some of the interesting circuit nodes. > > Regular scope probes don't work at ps speeds, and probe grounding is > > difficult. There are multi-GHz active probes, at roughly $1 per Hz. > > > So I was thinking that I could add a small, 0603 maybe, resistor to a > > signal to be snooped, run a 50 ohm trace some small distance, and end > > up at some structure that had a signal test point and a ground. > > Something roughly like this: > > >http://db.tt/6rRcagTt > > > The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. > > > The "probe" would be a piece of hardline coax that runs to a sampling > > scope input, with some provision for grounding. Something like a 3-5 > > GHz bandwidth should be feasible. > > > This looks promising if a little klunky. Any other ideas? > > something like this:http://www.idinet.com/IdiNet/media/PDF/94.pdf?ext=3D.=pdf> > think mouser have them > > -Lasse- Hide quoted text - > > - Show quoted text -Yup, I was going to suggest a connector if you've got room. Maybe just a ground ring on top for the hardline.. and some sort of springie contact for the signal on the bottom. gnd-----. .----gnd-- | | |.-- | -----*| *------ ----+ ^ +-springie contanct (phospur bronze?) George H.
Reply by ●February 12, 20122012-02-12
Okkim Atnarivik wrote:> > Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > : Looks good. Another approach would be something like a BFP650 follower, > > Phil, I was about to suggest that if you've ended up using the > BFP650 by following my example, you might be better off with the BFP640. > Or more modern ones with a higher hFE (I'm fond of the NESG3031 and > NESG4030). > > Namely, my choice of BFP650 (and not the then more widely available > BFP640) was driven by the search of the lowest possible R_BB, because > I was deemed to encounter lower source resistances than the 50ohms for > which SiGe devices are generally optimized. I reasoned that the base > geometry of the BFP650, as a medium power device, is more likely yield > a low R_BB. In your applications BFP640 may work better with the "more > ordinary" impedance levels and ambient temperatures. > > The "I was about.." part means that I'm somewhat puzzled now that I > looked up the recent Infineon data sheets. The BFP650 is now listed > as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon > model reads RB=6.376 . The preliminary datasheet I have, dated > Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm > wondering how much the device has changed from the versions I've been > using. I seem to recall that also in some other more recent data sheet > versions it was listed as a SiGe, not SiGe:C . > > Given the fact that the most recent BFP640 datasheet (dated 2007-05-29) > reads RB=3.129, the BFP650 does not seem to have any noise advantage > any more, either. > > In fact, there was a recent paper in the RSI where > the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe, > as compared with my 75 pV/rtHz with BFP650. This is a puzzling result, > actually, because it is better than one would expect in the picture where > u_N originates from the collector shot noise acting on the r_E - provided > that the thermal voltage saturates at ~5..7 meV even when the ambient > temperature keeps going down. According to my data it does saturate in > BFP640 just like it does in all other SiGe's I've tried, when measured by > the transconductance. I'm wondering whether my transistors have always > been oscillating so high that I cannot see it (ie. >27 GHz) and the > V_T saturation is an artefact due to it... > > Regards, > MikkoI started by taking your advice, which was pretty valuable--thanks again. I noticed the change in specs as well, when I ordered another batch a couple of months ago. They changed the type number to BFP650H instead of BFP650E when they changed the process. (The dogs.) I'm using it as a cascode stage for a SKY65050 pHEMT, and it works great. One of the best things about it is that it has effectively infinite Early voltage, so you can get a lot of voltage gain out of a single stage. Even for situations where you don't care so much about ultralow noise, the combination of a gigantic f_T with a very high V_A is unique in my collection. It does want to oscillate at 14 GHz if you look at it crosswise, but a nice 5-ohm bead in series with the base cleans that right up. I'm going to be using it in a new front end design, as a bootstrapped-bootstrap wrapped round a couple of parallelled BF862s. DC coupling the bootstrap and using a current source load gets rid of the thermal tails on the BF862s by keeping their dissipation constant. (Running them just slightly above I_DSS gives them a zero tempco anyway, but this one needs really good dc stability.) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 12, 20122012-02-12
On Sun, 12 Feb 2012 13:39:37 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Okkim Atnarivik wrote: >> >> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >> : Looks good. Another approach would be something like a BFP650 follower, >> >> Phil, I was about to suggest that if you've ended up using the >> BFP650 by following my example, you might be better off with the BFP640. >> Or more modern ones with a higher hFE (I'm fond of the NESG3031 and >> NESG4030). >> >> Namely, my choice of BFP650 (and not the then more widely available >> BFP640) was driven by the search of the lowest possible R_BB, because >> I was deemed to encounter lower source resistances than the 50ohms for >> which SiGe devices are generally optimized. I reasoned that the base >> geometry of the BFP650, as a medium power device, is more likely yield >> a low R_BB. In your applications BFP640 may work better with the "more >> ordinary" impedance levels and ambient temperatures. >> >> The "I was about.." part means that I'm somewhat puzzled now that I >> looked up the recent Infineon data sheets. The BFP650 is now listed >> as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon >> model reads RB=6.376 . The preliminary datasheet I have, dated >> Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm >> wondering how much the device has changed from the versions I've been >> using. I seem to recall that also in some other more recent data sheet >> versions it was listed as a SiGe, not SiGe:C . >> >> Given the fact that the most recent BFP640 datasheet (dated 2007-05-29) >> reads RB=3.129, the BFP650 does not seem to have any noise advantage >> any more, either. >> >> In fact, there was a recent paper in the RSI where >> the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe, >> as compared with my 75 pV/rtHz with BFP650. This is a puzzling result, >> actually, because it is better than one would expect in the picture where >> u_N originates from the collector shot noise acting on the r_E - provided >> that the thermal voltage saturates at ~5..7 meV even when the ambient >> temperature keeps going down. According to my data it does saturate in >> BFP640 just like it does in all other SiGe's I've tried, when measured by >> the transconductance. I'm wondering whether my transistors have always >> been oscillating so high that I cannot see it (ie. >27 GHz) and the >> V_T saturation is an artefact due to it... >> >> Regards, >> Mikko > >I started by taking your advice, which was pretty valuable--thanks >again. I noticed the change in specs as well, when I ordered another >batch a couple of months ago. They changed the type number to BFP650H >instead of BFP650E when they changed the process. (The dogs.) > >I'm using it as a cascode stage for a SKY65050 pHEMT, and it works >great. One of the best things about it is that it has effectively >infinite Early voltage, so you can get a lot of voltage gain out of a >single stage. Even for situations where you don't care so much about >ultralow noise, the combination of a gigantic f_T with a very high V_A >is unique in my collection. It does want to oscillate at 14 GHz if you >look at it crosswise, but a nice 5-ohm bead in series with the base >cleans that right up. > >I'm going to be using it in a new front end design, as a >bootstrapped-bootstrap wrapped round a couple of parallelled BF862s. DC >coupling the bootstrap and using a current source load gets rid of the >thermal tails on the BF862s by keeping their dissipation constant. >(Running them just slightly above I_DSS gives them a zero tempco anyway, >but this one needs really good dc stability.) > >Cheers > >Phil HobbsFunny you should say "cascode." I was just about to post the following: If I want a fast, low-capacitance, accurate, positive current source, I could build a fairly slow active current source with a voltage reference, a resistor, an opamp, and a p-fet. But it would have a lot of capacitance and would be fairly slow. So I could cascode that with a microwave-type PNP transistor, with a bit of base resistance or a ferrite bead to keep it stable. But then I'd have the base current error, and the good fast PNPs, what few there are, have mediocre betas. A PNP darlington is too slow. So, how to correct for the base current error? Two ideas so far: make a Darlington, but add a lowpass filter from the higher-current transistor base, into the emitter of the second transistor. The main transistor needed a base resistor anyhow. Or sense the base current of the PNP, with opamps and such, and increase the current of the precision/slow source to make up for it. -- John Larkin, President Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●February 12, 20122012-02-12
John Larkin a �crit :> On Sun, 12 Feb 2012 13:39:37 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Okkim Atnarivik wrote: >>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> : Looks good. Another approach would be something like a BFP650 follower, >>> >>> Phil, I was about to suggest that if you've ended up using the >>> BFP650 by following my example, you might be better off with the BFP640. >>> Or more modern ones with a higher hFE (I'm fond of the NESG3031 and >>> NESG4030). >>> >>> Namely, my choice of BFP650 (and not the then more widely available >>> BFP640) was driven by the search of the lowest possible R_BB, because >>> I was deemed to encounter lower source resistances than the 50ohms for >>> which SiGe devices are generally optimized. I reasoned that the base >>> geometry of the BFP650, as a medium power device, is more likely yield >>> a low R_BB. In your applications BFP640 may work better with the "more >>> ordinary" impedance levels and ambient temperatures. >>> >>> The "I was about.." part means that I'm somewhat puzzled now that I >>> looked up the recent Infineon data sheets. The BFP650 is now listed >>> as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon >>> model reads RB=6.376 . The preliminary datasheet I have, dated >>> Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm >>> wondering how much the device has changed from the versions I've been >>> using. I seem to recall that also in some other more recent data sheet >>> versions it was listed as a SiGe, not SiGe:C . >>> >>> Given the fact that the most recent BFP640 datasheet (dated 2007-05-29) >>> reads RB=3.129, the BFP650 does not seem to have any noise advantage >>> any more, either. >>> >>> In fact, there was a recent paper in the RSI where >>> the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe, >>> as compared with my 75 pV/rtHz with BFP650. This is a puzzling result, >>> actually, because it is better than one would expect in the picture where >>> u_N originates from the collector shot noise acting on the r_E - provided >>> that the thermal voltage saturates at ~5..7 meV even when the ambient >>> temperature keeps going down. According to my data it does saturate in >>> BFP640 just like it does in all other SiGe's I've tried, when measured by >>> the transconductance. I'm wondering whether my transistors have always >>> been oscillating so high that I cannot see it (ie. >27 GHz) and the >>> V_T saturation is an artefact due to it... >>> >>> Regards, >>> Mikko >> I started by taking your advice, which was pretty valuable--thanks >> again. I noticed the change in specs as well, when I ordered another >> batch a couple of months ago. They changed the type number to BFP650H >> instead of BFP650E when they changed the process. (The dogs.) >> >> I'm using it as a cascode stage for a SKY65050 pHEMT, and it works >> great. One of the best things about it is that it has effectively >> infinite Early voltage, so you can get a lot of voltage gain out of a >> single stage. Even for situations where you don't care so much about >> ultralow noise, the combination of a gigantic f_T with a very high V_A >> is unique in my collection. It does want to oscillate at 14 GHz if you >> look at it crosswise, but a nice 5-ohm bead in series with the base >> cleans that right up. >> >> I'm going to be using it in a new front end design, as a >> bootstrapped-bootstrap wrapped round a couple of parallelled BF862s. DC >> coupling the bootstrap and using a current source load gets rid of the >> thermal tails on the BF862s by keeping their dissipation constant. >> (Running them just slightly above I_DSS gives them a zero tempco anyway, >> but this one needs really good dc stability.) >> >> Cheers >> >> Phil Hobbs > > > Funny you should say "cascode." I was just about to post the > following: > > If I want a fast, low-capacitance, accurate, positive current source, > I could build a fairly slow active current source with a voltage > reference, a resistor, an opamp, and a p-fet. But it would have a lot > of capacitance and would be fairly slow. So I could cascode that with > a microwave-type PNP transistor, with a bit of base resistance or a > ferrite bead to keep it stable. But then I'd have the base current > error, and the good fast PNPs, what few there are, have mediocre > betas. > > A PNP darlington is too slow. > > So, how to correct for the base current error? >Try this : Ic = 3mA 1K | ___ |/ 5V>-----|___|----+------| | |> .-. | | | | 1K | | | '-' | | | |\ | ||-+ 3V>--|+\ | ||<- | >---------|-----||-+ .-|-/ | | | |/ | ___ | '--------------+--|___|-+ | 1K .-. | | | |1K '-' | === GND Delta Ic < 3nA for 45<Beta<65 for ex. -- Thanks, Fred.
Reply by ●February 12, 20122012-02-12
Fred Bartoli a �crit :> John Larkin a �crit : >> On Sun, 12 Feb 2012 13:39:37 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Okkim Atnarivik wrote: >>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> : Looks good. Another approach would be something like a BFP650 >>>> follower, >>>> >>>> Phil, I was about to suggest that if you've ended up using the >>>> BFP650 by following my example, you might be better off with the >>>> BFP640. >>>> Or more modern ones with a higher hFE (I'm fond of the NESG3031 and >>>> NESG4030). >>>> >>>> Namely, my choice of BFP650 (and not the then more widely available >>>> BFP640) was driven by the search of the lowest possible R_BB, because >>>> I was deemed to encounter lower source resistances than the 50ohms for >>>> which SiGe devices are generally optimized. I reasoned that the base >>>> geometry of the BFP650, as a medium power device, is more likely yield >>>> a low R_BB. In your applications BFP640 may work better with the "more >>>> ordinary" impedance levels and ambient temperatures. >>>> >>>> The "I was about.." part means that I'm somewhat puzzled now that I >>>> looked up the recent Infineon data sheets. The BFP650 is now listed >>>> as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon >>>> model reads RB=6.376 . The preliminary datasheet I have, dated >>>> Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm >>>> wondering how much the device has changed from the versions I've been >>>> using. I seem to recall that also in some other more recent data sheet >>>> versions it was listed as a SiGe, not SiGe:C . >>>> >>>> Given the fact that the most recent BFP640 datasheet (dated >>>> 2007-05-29) >>>> reads RB=3.129, the BFP650 does not seem to have any noise advantage >>>> any more, either. >>>> >>>> In fact, there was a recent paper in the RSI where >>>> the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe, >>>> as compared with my 75 pV/rtHz with BFP650. This is a puzzling result, >>>> actually, because it is better than one would expect in the picture >>>> where >>>> u_N originates from the collector shot noise acting on the r_E - >>>> provided >>>> that the thermal voltage saturates at ~5..7 meV even when the ambient >>>> temperature keeps going down. According to my data it does saturate in >>>> BFP640 just like it does in all other SiGe's I've tried, when >>>> measured by >>>> the transconductance. I'm wondering whether my transistors have always >>>> been oscillating so high that I cannot see it (ie. >27 GHz) and the >>>> V_T saturation is an artefact due to it... >>>> >>>> Regards, >>>> Mikko >>> I started by taking your advice, which was pretty valuable--thanks >>> again. I noticed the change in specs as well, when I ordered another >>> batch a couple of months ago. They changed the type number to BFP650H >>> instead of BFP650E when they changed the process. (The dogs.) >>> >>> I'm using it as a cascode stage for a SKY65050 pHEMT, and it works >>> great. One of the best things about it is that it has effectively >>> infinite Early voltage, so you can get a lot of voltage gain out of a >>> single stage. Even for situations where you don't care so much about >>> ultralow noise, the combination of a gigantic f_T with a very high V_A >>> is unique in my collection. It does want to oscillate at 14 GHz if you >>> look at it crosswise, but a nice 5-ohm bead in series with the base >>> cleans that right up. >>> I'm going to be using it in a new front end design, as a >>> bootstrapped-bootstrap wrapped round a couple of parallelled BF862s. DC >>> coupling the bootstrap and using a current source load gets rid of the >>> thermal tails on the BF862s by keeping their dissipation constant. >>> (Running them just slightly above I_DSS gives them a zero tempco anyway, >>> but this one needs really good dc stability.) >>> >>> Cheers >>> >>> Phil Hobbs >> >> >> Funny you should say "cascode." I was just about to post the >> following: >> >> If I want a fast, low-capacitance, accurate, positive current source, >> I could build a fairly slow active current source with a voltage >> reference, a resistor, an opamp, and a p-fet. But it would have a lot >> of capacitance and would be fairly slow. So I could cascode that with >> a microwave-type PNP transistor, with a bit of base resistance or a >> ferrite bead to keep it stable. But then I'd have the base current >> error, and the good fast PNPs, what few there are, have mediocre >> betas. >> >> A PNP darlington is too slow. >> >> So, how to correct for the base current error? > > Try this : > > > > > > Ic = 3mA > > 1K | > ___ |/ > 5V>-----|___|----+------| > | |> > .-. | > | | | > 1K | | | > '-' | > | | > |\ | ||-+ > 3V>--|+\ | ||<- > | >---------|-----||-+ > .-|-/ | | > | |/ | ___ | > '--------------+--|___|-+ > | > 1K .-. > | | > | |1K > '-' > | > === > GND > > > Delta Ic < 3nA for 45<Beta<65 for ex. >That is 3nA for an opamp with 10K DC gain, 300pA for 100K,... Maybe I should patent it and license it for one beer? Oops, too late... -- Thanks, Fred.
Reply by ●February 12, 20122012-02-12
On Sun, 12 Feb 2012 22:49:26 +0100, Fred Bartoli <" "> wrote:>John Larkin a �crit : >> On Sun, 12 Feb 2012 13:39:37 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Okkim Atnarivik wrote: >>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> : Looks good. Another approach would be something like a BFP650 follower, >>>> >>>> Phil, I was about to suggest that if you've ended up using the >>>> BFP650 by following my example, you might be better off with the BFP640. >>>> Or more modern ones with a higher hFE (I'm fond of the NESG3031 and >>>> NESG4030). >>>> >>>> Namely, my choice of BFP650 (and not the then more widely available >>>> BFP640) was driven by the search of the lowest possible R_BB, because >>>> I was deemed to encounter lower source resistances than the 50ohms for >>>> which SiGe devices are generally optimized. I reasoned that the base >>>> geometry of the BFP650, as a medium power device, is more likely yield >>>> a low R_BB. In your applications BFP640 may work better with the "more >>>> ordinary" impedance levels and ambient temperatures. >>>> >>>> The "I was about.." part means that I'm somewhat puzzled now that I >>>> looked up the recent Infineon data sheets. The BFP650 is now listed >>>> as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon >>>> model reads RB=6.376 . The preliminary datasheet I have, dated >>>> Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm >>>> wondering how much the device has changed from the versions I've been >>>> using. I seem to recall that also in some other more recent data sheet >>>> versions it was listed as a SiGe, not SiGe:C . >>>> >>>> Given the fact that the most recent BFP640 datasheet (dated 2007-05-29) >>>> reads RB=3.129, the BFP650 does not seem to have any noise advantage >>>> any more, either. >>>> >>>> In fact, there was a recent paper in the RSI where >>>> the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe, >>>> as compared with my 75 pV/rtHz with BFP650. This is a puzzling result, >>>> actually, because it is better than one would expect in the picture where >>>> u_N originates from the collector shot noise acting on the r_E - provided >>>> that the thermal voltage saturates at ~5..7 meV even when the ambient >>>> temperature keeps going down. According to my data it does saturate in >>>> BFP640 just like it does in all other SiGe's I've tried, when measured by >>>> the transconductance. I'm wondering whether my transistors have always >>>> been oscillating so high that I cannot see it (ie. >27 GHz) and the >>>> V_T saturation is an artefact due to it... >>>> >>>> Regards, >>>> Mikko >>> I started by taking your advice, which was pretty valuable--thanks >>> again. I noticed the change in specs as well, when I ordered another >>> batch a couple of months ago. They changed the type number to BFP650H >>> instead of BFP650E when they changed the process. (The dogs.) >>> >>> I'm using it as a cascode stage for a SKY65050 pHEMT, and it works >>> great. One of the best things about it is that it has effectively >>> infinite Early voltage, so you can get a lot of voltage gain out of a >>> single stage. Even for situations where you don't care so much about >>> ultralow noise, the combination of a gigantic f_T with a very high V_A >>> is unique in my collection. It does want to oscillate at 14 GHz if you >>> look at it crosswise, but a nice 5-ohm bead in series with the base >>> cleans that right up. >>> >>> I'm going to be using it in a new front end design, as a >>> bootstrapped-bootstrap wrapped round a couple of parallelled BF862s. DC >>> coupling the bootstrap and using a current source load gets rid of the >>> thermal tails on the BF862s by keeping their dissipation constant. >>> (Running them just slightly above I_DSS gives them a zero tempco anyway, >>> but this one needs really good dc stability.) >>> >>> Cheers >>> >>> Phil Hobbs >> >> >> Funny you should say "cascode." I was just about to post the >> following: >> >> If I want a fast, low-capacitance, accurate, positive current source, >> I could build a fairly slow active current source with a voltage >> reference, a resistor, an opamp, and a p-fet. But it would have a lot >> of capacitance and would be fairly slow. So I could cascode that with >> a microwave-type PNP transistor, with a bit of base resistance or a >> ferrite bead to keep it stable. But then I'd have the base current >> error, and the good fast PNPs, what few there are, have mediocre >> betas. >> >> A PNP darlington is too slow. >> >> So, how to correct for the base current error? >> > >Try this : > > > > > > Ic = 3mA > > 1K | > ___ |/ > 5V>-----|___|----+------| > | |> > .-. | > | | | > 1K | | | > '-' | > | | > |\ | ||-+ > 3V>--|+\ | ||<- > | >---------|-----||-+ > .-|-/ | | > | |/ | ___ | > '--------------+--|___|-+ > | > 1K .-. > | | > | |1K > '-' > | > === > GND > > >Delta Ic < 3nA for 45<Beta<65 for ex.Interesting cancellation of beta terms. But doesn't VAF of the NPN bung thing up? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●February 12, 20122012-02-12
Fred Bartoli wrote:> > Fred Bartoli a �crit : > > John Larkin a �crit : > >> On Sun, 12 Feb 2012 13:39:37 -0500, Phil Hobbs > >> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> > >>> Okkim Atnarivik wrote: > >>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>>> : Looks good. Another approach would be something like a BFP650 > >>>> follower, > >>>> > >>>> Phil, I was about to suggest that if you've ended up using the > >>>> BFP650 by following my example, you might be better off with the > >>>> BFP640. > >>>> Or more modern ones with a higher hFE (I'm fond of the NESG3031 and > >>>> NESG4030). > >>>> > >>>> Namely, my choice of BFP650 (and not the then more widely available > >>>> BFP640) was driven by the search of the lowest possible R_BB, because > >>>> I was deemed to encounter lower source resistances than the 50ohms for > >>>> which SiGe devices are generally optimized. I reasoned that the base > >>>> geometry of the BFP650, as a medium power device, is more likely yield > >>>> a low R_BB. In your applications BFP640 may work better with the "more > >>>> ordinary" impedance levels and ambient temperatures. > >>>> > >>>> The "I was about.." part means that I'm somewhat puzzled now that I > >>>> looked up the recent Infineon data sheets. The BFP650 is now listed > >>>> as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon > >>>> model reads RB=6.376 . The preliminary datasheet I have, dated > >>>> Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm > >>>> wondering how much the device has changed from the versions I've been > >>>> using. I seem to recall that also in some other more recent data sheet > >>>> versions it was listed as a SiGe, not SiGe:C . > >>>> > >>>> Given the fact that the most recent BFP640 datasheet (dated > >>>> 2007-05-29) > >>>> reads RB=3.129, the BFP650 does not seem to have any noise advantage > >>>> any more, either. > >>>> > >>>> In fact, there was a recent paper in the RSI where > >>>> the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe, > >>>> as compared with my 75 pV/rtHz with BFP650. This is a puzzling result, > >>>> actually, because it is better than one would expect in the picture > >>>> where > >>>> u_N originates from the collector shot noise acting on the r_E - > >>>> provided > >>>> that the thermal voltage saturates at ~5..7 meV even when the ambient > >>>> temperature keeps going down. According to my data it does saturate in > >>>> BFP640 just like it does in all other SiGe's I've tried, when > >>>> measured by > >>>> the transconductance. I'm wondering whether my transistors have always > >>>> been oscillating so high that I cannot see it (ie. >27 GHz) and the > >>>> V_T saturation is an artefact due to it... > >>>> > >>>> Regards, > >>>> Mikko > >>> I started by taking your advice, which was pretty valuable--thanks > >>> again. I noticed the change in specs as well, when I ordered another > >>> batch a couple of months ago. They changed the type number to BFP650H > >>> instead of BFP650E when they changed the process. (The dogs.) > >>> > >>> I'm using it as a cascode stage for a SKY65050 pHEMT, and it works > >>> great. One of the best things about it is that it has effectively > >>> infinite Early voltage, so you can get a lot of voltage gain out of a > >>> single stage. Even for situations where you don't care so much about > >>> ultralow noise, the combination of a gigantic f_T with a very high V_A > >>> is unique in my collection. It does want to oscillate at 14 GHz if you > >>> look at it crosswise, but a nice 5-ohm bead in series with the base > >>> cleans that right up. > >>> I'm going to be using it in a new front end design, as a > >>> bootstrapped-bootstrap wrapped round a couple of parallelled BF862s. DC > >>> coupling the bootstrap and using a current source load gets rid of the > >>> thermal tails on the BF862s by keeping their dissipation constant. > >>> (Running them just slightly above I_DSS gives them a zero tempco anyway, > >>> but this one needs really good dc stability.) > >>> > >>> Cheers > >>> > >>> Phil Hobbs > >> > >> > >> Funny you should say "cascode." I was just about to post the > >> following: > >> > >> If I want a fast, low-capacitance, accurate, positive current source, > >> I could build a fairly slow active current source with a voltage > >> reference, a resistor, an opamp, and a p-fet. But it would have a lot > >> of capacitance and would be fairly slow. So I could cascode that with > >> a microwave-type PNP transistor, with a bit of base resistance or a > >> ferrite bead to keep it stable. But then I'd have the base current > >> error, and the good fast PNPs, what few there are, have mediocre > >> betas. > >> > >> A PNP darlington is too slow. > >> > >> So, how to correct for the base current error? > > > > Try this : > > > > > > > > > > > > Ic = 3mA > > > > 1K | > > ___ |/ > > 5V>-----|___|----+------| > > | |> > > .-. | > > | | | > > 1K | | | > > '-' | > > | | > > |\ | ||-+ > > 3V>--|+\ | ||<- > > | >---------|-----||-+ > > .-|-/ | | > > | |/ | ___ | > > '--------------+--|___|-+ > > | > > 1K .-. > > | | > > | |1K > > '-' > > | > > === > > GND > > > > > > Delta Ic < 3nA for 45<Beta<65 for ex. > > > > That is 3nA for an opamp with 10K DC gain, 300pA for 100K,... > > Maybe I should patent it and license it for one beer? > > Oops, too late... > > -- > Thanks, > Fred.Cute! Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 12, 20122012-02-12
Jim Thompson wrote:> > On Sun, 12 Feb 2012 22:49:26 +0100, Fred Bartoli <" "> wrote: > > >John Larkin a �crit : > >> On Sun, 12 Feb 2012 13:39:37 -0500, Phil Hobbs > >> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> > >>> Okkim Atnarivik wrote: > >>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>>> : Looks good. Another approach would be something like a BFP650 follower, > >>>> > >>>> Phil, I was about to suggest that if you've ended up using the > >>>> BFP650 by following my example, you might be better off with the BFP640. > >>>> Or more modern ones with a higher hFE (I'm fond of the NESG3031 and > >>>> NESG4030). > >>>> > >>>> Namely, my choice of BFP650 (and not the then more widely available > >>>> BFP640) was driven by the search of the lowest possible R_BB, because > >>>> I was deemed to encounter lower source resistances than the 50ohms for > >>>> which SiGe devices are generally optimized. I reasoned that the base > >>>> geometry of the BFP650, as a medium power device, is more likely yield > >>>> a low R_BB. In your applications BFP640 may work better with the "more > >>>> ordinary" impedance levels and ambient temperatures. > >>>> > >>>> The "I was about.." part means that I'm somewhat puzzled now that I > >>>> looked up the recent Infineon data sheets. The BFP650 is now listed > >>>> as a SiGe:C part (the datasheet 2010-10-22) and its Gummel-Poon > >>>> model reads RB=6.376 . The preliminary datasheet I have, dated > >>>> Aug-16-2004, lists it as an ordinary SiGe part with RB=1.036 . So, I'm > >>>> wondering how much the device has changed from the versions I've been > >>>> using. I seem to recall that also in some other more recent data sheet > >>>> versions it was listed as a SiGe, not SiGe:C . > >>>> > >>>> Given the fact that the most recent BFP640 datasheet (dated 2007-05-29) > >>>> reads RB=3.129, the BFP650 does not seem to have any noise advantage > >>>> any more, either. > >>>> > >>>> In fact, there was a recent paper in the RSI where > >>>> the Jena group claim to have achieved 15 pV/rtHz with BFP640 in LHe, > >>>> as compared with my 75 pV/rtHz with BFP650. This is a puzzling result, > >>>> actually, because it is better than one would expect in the picture where > >>>> u_N originates from the collector shot noise acting on the r_E - provided > >>>> that the thermal voltage saturates at ~5..7 meV even when the ambient > >>>> temperature keeps going down. According to my data it does saturate in > >>>> BFP640 just like it does in all other SiGe's I've tried, when measured by > >>>> the transconductance. I'm wondering whether my transistors have always > >>>> been oscillating so high that I cannot see it (ie. >27 GHz) and the > >>>> V_T saturation is an artefact due to it... > >>>> > >>>> Regards, > >>>> Mikko > >>> I started by taking your advice, which was pretty valuable--thanks > >>> again. I noticed the change in specs as well, when I ordered another > >>> batch a couple of months ago. They changed the type number to BFP650H > >>> instead of BFP650E when they changed the process. (The dogs.) > >>> > >>> I'm using it as a cascode stage for a SKY65050 pHEMT, and it works > >>> great. One of the best things about it is that it has effectively > >>> infinite Early voltage, so you can get a lot of voltage gain out of a > >>> single stage. Even for situations where you don't care so much about > >>> ultralow noise, the combination of a gigantic f_T with a very high V_A > >>> is unique in my collection. It does want to oscillate at 14 GHz if you > >>> look at it crosswise, but a nice 5-ohm bead in series with the base > >>> cleans that right up. > >>> > >>> I'm going to be using it in a new front end design, as a > >>> bootstrapped-bootstrap wrapped round a couple of parallelled BF862s. DC > >>> coupling the bootstrap and using a current source load gets rid of the > >>> thermal tails on the BF862s by keeping their dissipation constant. > >>> (Running them just slightly above I_DSS gives them a zero tempco anyway, > >>> but this one needs really good dc stability.) > >>> > >>> Cheers > >>> > >>> Phil Hobbs > >> > >> > >> Funny you should say "cascode." I was just about to post the > >> following: > >> > >> If I want a fast, low-capacitance, accurate, positive current source, > >> I could build a fairly slow active current source with a voltage > >> reference, a resistor, an opamp, and a p-fet. But it would have a lot > >> of capacitance and would be fairly slow. So I could cascode that with > >> a microwave-type PNP transistor, with a bit of base resistance or a > >> ferrite bead to keep it stable. But then I'd have the base current > >> error, and the good fast PNPs, what few there are, have mediocre > >> betas. > >> > >> A PNP darlington is too slow. > >> > >> So, how to correct for the base current error? > >> > > > >Try this : > > > > > > > > > > > > Ic = 3mA > > > > 1K | > > ___ |/ > > 5V>-----|___|----+------| > > | |> > > .-. | > > | | | > > 1K | | | > > '-' | > > | | > > |\ | ||-+ > > 3V>--|+\ | ||<- > > | >---------|-----||-+ > > .-|-/ | | > > | |/ | ___ | > > '--------------+--|___|-+ > > | > > 1K .-. > > | | > > | |1K > > '-' > > | > > === > > GND > > > > > >Delta Ic < 3nA for 45<Beta<65 for ex. > > Interesting cancellation of beta terms. But doesn't VAF of the NPN > bung thing up?If you use a BFP650, VAF is huge (or even negative), even with a 40 GHz f_T. See Figure 3 on the datasheet, http://tinyurl.com/6rkavak Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
